This invention relates to a VoIP terminal speech quality control system and method that can guarantee speech quality without failing in switching back even if a VoIP terminal is resumed after holding and further that can secure a speech band at a handover destination AP even if the VoIP terminal hands over during holding, thereby guaranteeing speech quality without failing in switching back even if the VoIP terminal is resumed after the holding, and further relates to a program that causes a computer to execute such a method and a recording medium recording such a program.
In real-time communications such as VoIP (Voice over IP) communications in the conventional wireless LAN (Local Area Network) system, a band of an access point (hereinafter referred to as an “AP”) is congested to cause delay or discard of packets as the number of communications increases, so that there occurs a phenomenon such as pauses in communication. Therefore, it has been difficult to perform comfortable communications.
For solving such a problem, there is known, for example, a technique that provides a limit to the number of VoIP calls under the control of the same AP and transmits a Dis-Association frame to an outgoing call (or an incoming call) of a VoIP terminal exceeding the limited number to refuse communication, thereby preventing exceeding the limited number to realize high-quality speeches.
That is, under the control of the AP having the call number control function, holding is not recognized as a call and, when the number of calls reaches the maximum, i.e. the limited number, a call is disconnected or released after resumption subsequent to the holding.
As related prior art, see a prior art document (Japanese Unexamined Patent Application Publication No. Hei 05-284097).
However, the foregoing conventional technique has the following problems.
In an environment where a single AP is present, a RTP (Realtime Transport Protocol) communication is not performed when a terminal is in holding. Therefore, the number of calls is reduced by one. Then, when the number of calls reaches the maximum during the holding, a Dis-Association frame is sent in reply to an outgoing call (or an incoming call) in resumption subsequent to the holding, so that a handover occurs. Accordingly, after AP searching, a Dis-Association frame is received again and, finally, switching back is disabled due to time-out. This problem is solved if the AP has a SIP (Session Initiation Protocol) proxy function. However, adding the SIP proxy function to the AP causes a high cost due to advanced hardware functionality. Further, there also arises a problem that connectable SIP servers are limited.
On the other hand, in an environment where a plurality of APs are present, when a terminal hands over from one AP to another during holding, if the number of calls is full at the handover destination AP, resumption after the holding is disabled and thus the communication is disconnected. This problem can be solved if there is a product having a WLAN controller adapted to control between the APs. However, there arises a problem that this product causes a high cost.